At present, a liquid crystal displays (LCD) exemplified by a TFT-LCD has become one very important type of flat panel displays and has attracted extensive attention. During manufacture of a TFT-LCD, efforts have been made to adopt a more advanced manufacturing method, simplify producing process, and reduce production cost. Among the others, simplification of process and the reduction of production cost for each device of a TFT-LCD directly lead to the simplification of manufacturing process and the reduction of production cost of the whole TFT-LCD.
A LCD generally comprises an upper substrate and a lower substrate which are joined together by a seal agent. Electrodes are formed on the upper and lower substrates, and liquid crystal material is filled between the two substrates. Particles of a certain diameter are distributed between the two substrates to maintain a constant gap between the two substrates. A thin film transistor (TFT) is formed on the surface of the lower substrate as a switching element. The TFT can comprise a gate electrode connected with a gate line, a source electrode connected with a signal line, and a drain electrode connected with a pixel electrode. Specifically, the TFTs used for a TFT-LCD commonly comprise a gate electrode which may be a portion of the gate line, an active layer (comprising a semiconductor layer and a doped semiconductor layer) which forms a channel, a source electrode which may be a portion of the data line, and a drain electrode which opposes the source on the active layer and is electrically connected with the pixel electrode. The TFT, as a switching element, controls, under the electrical signal transmitted to the gate electrode through the gate line, the transmission of the data signal transmitted through the data line to the pixel electrode.
In recent years, in a conventional method of manufacturing a TFT-LCD, an array forming process is widely used, in which patterning processes by photolithography with a mask are performed for several times on a glass base substrate to form a TFT array. Since the mask for exposing is very expensive, it is an efficient method to decrease production cost by reducing the times of photolithography with a mask. However, decrease of the times of photolithography with a mask may render other processes in manufacturing a TFT-LCD complicated and may even make impossible to carry out such processes.
One currently popular method of manufacturing a TFT-LCD is a four-mask method, in which photolithography processes are carried out for four times, for which four masks are needed. In addition, processes such as deposition, etching, and/or stripping are necessary for forming a pattern. In the four-mask manufacturing method, a gray tone mask technology can be used for etching to form the source/drain metal electrodes and the channel portion of the active layer of the TFT. The fabrication of these portions is the key for manufacturing a TFT-LCD, which, in practice, imposes rigorous requirements on etching selectivity and the photolithography process and further brings complication to the manufacturing process.
Therefore, there is a need for a method of manufacturing a TFT-LCD which uses less masks and which is also simple in procedure and easy to carry out.